A wide variety of improvements have been made in recent years in the eyewear field, particularly with respect to eyewear intended for use in active sports or as fashion sunglasses. These improvements have been incorporated into eyewear having a unitary lens, such as the "Blades.RTM." design (Oakley, Inc.) the "M Frame.RTM." line (Oakley, Inc.), and the "Zero.RTM." line also produced by Oakley, Inc. These eyewear designs accomplish a variety of functional advantages, such as maximizing interception of peripheral light, reducing optical distortion and increasing the wearer's comfort level, compared to previous active sport eyewear.
The unitary lens of the "Blades.RTM." eyewear incorporates the cylindrical geometry disclosed, for example, in U.S. Pat. No. 4,859,048, issued to Jannard. This geometry allows the lens to closely conform to the wearer's face and intercept light, wind, dust, etc. from directly in front of the wearer (anterior direction) and peripherally (lateral direction). See also U.S. Pat. No. 4,867,550 to Jannard (toroidal lens geometry).
Although the early unitary lens systems provided a full side-to-side range of vision and good lateral eye protection, the potential for optical distortion still exists. In a unitary lens system, for example, the angle of incidence from the wearer's eye to the posterior lens surface changes as the wearer's sight line turns in either the vertical or horizontal planes. This results in disparate refraction between light entering closer to the front of the lens and peripheral light entering at the lateral ends. To address this source of prismatic distortion, U.S. Pat. No. 4,859,048 discloses tapering the thickness of the lens from the medial portion toward the lateral edge.
Unitary lens goggles and protective helmet shields are subject to the same sources of optical distortion. A wide variety of goggle and helmet shields are known for such activities as motorcycle riding, skiing, football, lacrosse, hockey and the like. Unitary lenses are also found in underwater diving masks and a variety of industrial safety applications such as welding and for power equipment operators. While the state of the art in each of these applications has generally achieved the desired level of physical eye protection, the current products generally still exhibit relatively high prismatic distortion and sometimes also power and/or astigmatism.
Thus, there remains a need for a nonprescription shield for use in such applications as unitary lens eyeglasses and athletic safety helmets which can intercept light throughout both a vertical and horizontal angular range of vision while at the same time minimize optical distortion throughout that range.